Method of nitriding steel articles



Patented Feb. 25, 1930 UNITED STATES ROBERT SERGESON, OF MASSILLON, OHIO, ASSIGNOR TO CENTRAL ALLOY STEEL CORP PATENT, OFFICE PORATION, OF MASSILLON, OHIO, A. CORPORATION OF NEW YORK METHOD OF NITRIDING STEEL ARTICLES No Drawing.

This invention relates in general to the.

heat treatment of articles made from steel alloys, for the purpose of placing the articles in a condition to receive thereon a hard, tough, coherent case or coating, when the articles are subsequently nitrided, as by means of ammonia gas.

It has been observed in the nitriding of articles made f'romsteel alloys,that when these articles are nitrided in the as rolled or annealed condition, that the case or coating which is formed thereon is usually of an inferior character, that is to say, it is characterized by one or moreof the following defects:

(1) The depth of penetration of the case is not uniform.

(2) The case is brittle and does not properly adhere to the core.

In consequence of these defects, the articles, when dropped or subjected to abnormal stresses in service, frequently break or spall, and such occurrences have retarded the de velopment of the nitriding industry to a greater extent than any other single factor.

As a result of a series of experiments, which I have made, I have discovered that practically all of the aforesaid defects may be more or less completely obviated by subjecting the articles, prior to nitriding same, to a suitable heat treatment.

The character of the heat treatment varies to some extent with the analysis of the steel from which the articles are formed, but in all cases, the articles are uniformly heated to a temperature above their upper critical point and quenched in any suitable manner, as in oil or water. The articles are then drawn at a temperature below their lower critical point, and are then nitrided in the usual manner. s.

As a result of the aforesaid heat treatment, the case on the nitrided articles is found to harder, deeper and tougher than the case on articles nit-rided without previous heat treatment. The case adheres firmly to the core and the articles are immune in a high degree from failures due to breakage or spalling, when dropped or subjected to abnormal stresses in service.

In order to bring out the efiects of heat Application filed March 28, 1929. Serial No. 350,575.

As rolled" .010 85c Heat treated .913 1015 I- claim:

1. The method of nitriding articles made from steel alloys, which comprises heating the articles to a temperature above their upper critical point, quenching the articles, drawing the articles at a temperature below their lower critical point, and then nitriding the articles, the object of said heat treatment being to increase the depth and hardness of the nitrided case to a degree greater than is obtainable when the articles are nitrided without being thus previously heat treated.

2. The method of nitriding articles made from steel alloys, which comprises heating the articles to a temperature of about 165091 quenching the articles, drawing the articles at a temperature of about 1200911, and then m nitriding the articles, the object of said treatment being to increase the depth and hardness of the nitrided case to a degree greater than is obtainable when the articles are nitrided without. being thus previously heat treated.

In testimony whereof I affix my signature.

ROBERT SERGESUN.

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